1000# vs. 1400# bars?

[dznf0g]

First we have to determine EFFECTIVE spring bar length (not actual lengths commonly used in generic calculators)

First measure the actual bar length from half way through the front vertical section (the part in the bushings on the hitch head) to the CENTER of the device used to pull the rear end up (chain bracket, U-bolt, pin etc). The PP is 28.5" in actual length.

That measurement IS NOT a good length for your calculations, because the bars are splayed. Because of this, a portion of the bar end force is used up in trying to bend the hitch head in half, if you will, along its longitudinal centerline.

We are interested in the force required to return X weight down the centerline of the TV.

So, now that you have the actual length of the bars, measure the splay distance between the points where your chain, jacks, etc. pull up on the ends of the bars.

Now measure the distance between the CENTERS of the bushings for the spring bars in the hitch head. Subtract 50% of the bushing separation distance from the total splay distance. You now have the distance between the splayed bar end position and the spot where the bar is pointed down the centerline of the TV.

My Specs:

Actual bar length = 28.5
Bushing separation distance = 3"
Splay distance = 28"
distance of "swing" of bar end to bring it to centerline = 12.5" (28/2)-1.5

Since Asq +Bsq = Csq I have 12.5sq + Bsq = 28.5sq, or Bsq = 28.5sq-12.5sq

Or 812.25 - 156.25 = Bsq thus b = sq rt of 656, or 25.612 (that is the effective length of the spring bar as installed and hitched.

Understanding this is essential to spring bar selection. using the conventional generic spring bar length vs. actual effective spring bar length puts some in danger of undersizing their bar selection.

More to come, I gotta go for awhile.

[dznf0g]

Now, for the rest of the calculations, you need some weights and measures for your rig, as well as your TV mfr's desired weight (measure) return for the front axle for WD application. Mine is 50% of no WD and WD applied. I will use the weights and measures for my rig and you will have to determine your numbers to input to the calculations.

You will need:
(measurements)
wheel base (WB) of truck
rear axle to receiver mouth distance
receiver mouth to center-of-bushing distance
previously determined effective spring bar length
trailer axle(s) to receiver mouth distance

Accurate weights from scaling:
Discussed ad nauseum in other threads

My figures:

WB = 143.5
RA-to-RM = 47.24
Receiver mouth to Bushing = 8.25
effective bar length = 25.612
TA to receiver mouth = 243.245

I have discovered a "sweet spot" range for my PP jack setting from 3.5" to 4" of jack showing (V2 jacks) which represents varying loads in the trailer affecting TW on a given day. Your settings will obviously vary by hitch type and loading of trailer. I'll use 4" numbers to illustrate a singular setting. (note: my TV mfr states to adjust to a 50% measured distance return between no-WD and unhitched fender height....this Miraculously equals a 50% weight return...not really miraculous, there is a 1-1 correspondence whether you use measurement or weights. But you need weights for this exercise, since your desired result is spring bar end force, in pounds.

At 4" of WD, my actual scale tickets showed this:

FA = 3260
RA = 3660
TA = 7680

At no WD scale tickets showed

FA = 3100
RA = 3900
TA = 7600

FA return = 160
Removed from RA = 240
Shifted to TA = 80


So then, what is the spring bar end force to achieve those desired results?

Since we know our weight outcomes from the scale ticket, you can choose any of those 3 (FA, RA or TA) as input to your formula. I used TA, just because it is a less complicated formula to arrive at bar end force.

Spring bar end force = TA weight transfer/((effective spring bar length/(TA to Ball+2"))

Spring bar end force = 80/ ((25.612/(223.37+2))

Spring bar end force = 80/.11364

Spring bar end force = 704#

So with my current rig and setup, with 1k PP bars (2k total capacity...desired 1k static load) I am only at 35.2% of static capacity. It is obvious to me that 1400# bars are way too much.

If I chose 800# PP bars, I would be at 44% of static capacity and they would be fine...and more flexible, but what if my TW changes dramatically???

I do also have a Reese Dual cam with 800# bars, and the WD is fine, but by the seat-of-the-pants, on-the-fly "feel" it just seems a bit too close. I'd love to swap out for PP 800# bars and bushings and see, but don't want to spend the $$ for an experiment. PP and Reese bars are different in shape, taper and in length (slightly).

[A W Warn]

Don't forget to include the cargo weight that will loaded behind the axle when choosing the torsion bars.

Etrailer says: "the additional weight behind the rear axle from cargo gets counted as tongue weight when picking out a weight distribution system"

https://www.etrailer.com/question-345438.html

[dznf0g]

Originally Posted by A W Warn

Don't forget to include the cargo weight that will loaded behind the axle when choosing the torsion bars.

Etrailer says: "the additional weight behind the rear axle from cargo gets counted as tongue weight when picking out a weight distribution system"

https://www.etrailer.com/question-345438.html

It is accounted for when you weigh your rig with no WD vs. WD (or measure, for that matter). Assuming, the truck is loaded for camping when you weigh (or measure). The reason they point that out is you get a "double whammy" to the rear axle increase and thus FA decrease as that weight is cantilevered. But it isn't just an additive figure to a bar calculation. This is another "all encompassing" statement used because they don't know the discernment level of their audience....like a lot of the gross, or global audience statements made about hitching and WD.

And, I gotta tell you, in my fiddling with the numbers, unless you are loading a pallet of bricks, it has a much less effect on the bar end force required than one would think.

[Spaggs]

I don’t have a pallet of bricks, but the Excursion has a 44 gallon fuel tank and I plan on installing a couple of boxes on my rear bumper with a couple of Honda generators and a couple of 5 gallon fuel tanks. This will weigh in at 280 lbs. The rear bumper is an Aluminess with arms to hold the boxes.
Seems like the consensus is I should trade in my 1400s for the 1000s.

[dznf0g]

Originally Posted by Spaggs

I don’t have a pallet of bricks, but the Excursion has a 44 gallon fuel tank and I plan on installing a couple of boxes on my rear bumper with a couple of Honda generators and a couple of 5 gallon fuel tanks. This will weigh in at 280 lbs. The rear bumper is an Aluminess with arms to hold the boxes.

Seems like the consensus is I should trade in my 1400s for the 1000s.

I would, based on the limited information you have provided.

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[A W Warn]

Sorry, I did not make myself clear in my prior post.
I was speaking to the OP, who is still awaiting his trailer's delivery. He has no way to weigh it right now.

[dznf0g]

Originally Posted by A W Warn

Sorry, I did not make myself clear in my prior post.
I was speaking to the OP, who is still awaiting his trailer's delivery. He has no way to weigh it right now.

Gotcha. He could load his truck the way he "thinks" he will with the trailer (unknown TW, loaded) and weigh just it. That would give a somewhat closer SWAG before purchasing the hitch. Of course, some number noodling would have to follow that solo weighing.

[uncle_bob]

Originally Posted by dznf0g

Gotcha. He could load his truck the way he "thinks" he will with the trailer (unknown TW, loaded) and weigh just it. That would give a somewhat closer SWAG before purchasing the hitch. Of course, some number noodling would have to follow that solo weighing.

Hi

A lot of folks are in the same position. Trailer is on order, trying to fit a TV / hitch to that "unknown" trailer. As noted in a lot of places, unless you have something < 25' long, your AS likely will have a tongue weight up around 1,000 pounds. That's the starting point for the "fit" process.

Next part of the fit process would be to have at least 20% more payload on the TV than all the calculations suggest. There will be surprises, folks tend to underestimate things. Coming up with a stable ride may mean adjusting things a bit off of the "ideal" WD settings. You need some room.

Bars are sort of the opposite of payload. Unless you have maxed out a lower weight bar, there is no need to go to a heavier one. None of these outfits have one bar that stops working at 1000.001 pounds and another that starts working at 1000.0005. They all overlap a *lot*. Start with the smaller of the two likely candidates.

Understand the loading math on the trailer ( no water in any tank ) and on the TV ( people not already in the number ). There are lots of in's and outs in adding this all up. The surprises all seem to be in the "more weight" direction. Going over the calculations again and again is the only way to get close.

Fun

Bob

[dznf0g]

Originally Posted by uncle_bob

Hi

A lot of folks are in the same position. Trailer is on order, trying to fit a TV / hitch to that "unknown" trailer. As noted in a lot of places, unless you have something < 25' long, your AS likely will have a tongue weight up around 1,000 pounds. That's the starting point for the "fit" process.

Next part of the fit process would be to have at least 20% more payload on the TV than all the calculations suggest. There will be surprises, folks tend to underestimate things. Coming up with a stable ride may mean adjusting things a bit off of the "ideal" WD settings. You need some room.

Bars are sort of the opposite of payload. Unless you have maxed out a lower weight bar, there is no need to go to a heavier one. None of these outfits have one bar that stops working at 1000.001 pounds and another that starts working at 1000.0005. They all overlap a *lot*. Start with the smaller of the two likely candidates.

Understand the loading math on the trailer ( no water in any tank ) and on the TV ( people not already in the number ). There are lots of in's and outs in adding this all up. The surprises all seem to be in the "more weight" direction. Going over the calculations again and again is the only way to get close.

Fun

Bob

Yes ^

See a typical selection guide here. (scroll down)

https://www.propridehitch.com/propri...YaAuO-EALw_wcB

So, like most, Sean uses TW as a guide. Since one presumably has no hitch yet, if they are shopping this guide, I ASSUME his TW figures represent a loaded trailer with NO hitch components yet added to the weight mix.

So, if I apply my figures, as loaded and exemplified above, to his guide, I have a "naked" TW of 962# (done with a sherline) loaded for my 10 week trip next weekend).

You can see, by his chart, that firmly puts me in the 1K range (purple) and at the low end of the 1.4k range (blue). My own calculations (above) with fully loaded trailer and truck including occupants, water, etc., make me believe that he has slid the whole chart to the heavier recommendation side, per category, in order to compensate for the unknowns of most purchasers as to their true weights when their trailer arrives and is loaded.

Since my calculations above reveal a true bar force (direct relationship to bar capacity, instead of an inferred relationship of TW) of 704# with a 962# true naked, but loaded TW, you can get an idea of the wiggle room they install in their chart recommendations.

As I stated before, when I called Sean with all my numbers, he had no problem sliding his recommendation down from 1.4k bars to 1k bars. He would not go so far as to recommend to me to go down to 800# bars...even though I tried to communicate how closely I watch the numbers on a spreadsheet before and during travel.

[dznf0g]

One item if forgot to mention in post #22 (copied below) for those of you who might want to calculate. The 2" reference in the formulas is there because a PP and a Hensley have the bar bushing locations 2" FORWARD of the ball. PP is 2" and I think Hensley is too, but check. It seems most others are in line with the ball, but check and either delete the "+2" in the formula, or substitute your findings with your hitch.


"So then, what is the spring bar end force to achieve those desired results?

Since we know our weight outcomes from the scale ticket, you can choose any of those 3 (FA, RA or TA) as input to your formula. I used TA, just because it is a less complicated formula to arrive at bar end force.

Spring bar end force = TA weight transfer/((effective spring bar length/(TA to Ball+2"))

Spring bar end force = 80/ ((25.612/(223.37+2))

Spring bar end force = 80/.11364

Spring bar end force = 704#"

[uncle_bob]

Hi

The only reason you *need* WD is to balance the load on the TV. As long as WD and AS are completely separate functions, you are fine. Yes, if your hitch does AS and WD "all in one" (which the vast majority of them do) then that adds another layer to this.

If the rear axle on your truck can handle another thousand pounds ( think F350 dually ....) then away you go. No WD and no bars. The "spring" numbers are out of the picture. Do your AS by whatever magic you choose to use.

The *big* gotcha is that even with a fancy hitch, it never is 100% clear that WD and AS are totally separate. That's what a lot of folks claim, but I suspect there are interactions.

Bob

[dznf0g]

Originally Posted by uncle_bob

Hi

The only reason you *need* WD is to balance the load on the TV. As long as WD and AS are completely separate functions, you are fine. Yes, if your hitch does AS and WD "all in one" (which the vast majority of them do) then that adds another layer to this.

If the rear axle on your truck can handle another thousand pounds ( think F350 dually ....) then away you go. No WD and no bars. The "spring" numbers are out of the picture. Do your AS by whatever magic you choose to use.

The *big* gotcha is that even with a fancy hitch, it never is 100% clear that WD and AS are totally separate. That's what a lot of folks claim, but I suspect there are interactions.

Bob

If one has downward head tilt, then there is definitely an interaction between WD and sway control. No head tilt, no interaction....or maybe influence is a better word.

Edit: actually there is a bit of interaction with parallel bars, due to the arc swing of the tension jacks/chains, etc. during turns, but not a whole lot. Of course, elevation changes between TV axle(s) and trailer axle(s) come into play a bit too. (ie. not a dead flat turn)

[uncle_bob]

Originally Posted by dznf0g

If one has downward head tilt, then there is definitely an interaction between WD and sway control. No head tilt, no interaction....or maybe influence is a better word.

Edit: actually there is a bit of interaction with parallel bars, due to the arc swing of the tension jacks/chains, etc. during turns, but not a whole lot. Of course, elevation changes between TV axle(s) and trailer axle(s) come into play a bit too. (ie. not a dead flat turn)

Hi

You can have a downward tilt with a 5th wheel and not have a sway issue. If the Pro Pride and Hensley hitches fully emulate this, the same should be true of them.

Bob

[dznf0g]

Originally Posted by uncle_bob

Hi

You can have a downward tilt with a 5th wheel and not have a sway issue. If the Pro Pride and Hensley hitches fully emulate this, the same should be true of them.

Bob

5th wheel pin location is at, or slightly ahead of the rear axle centerline. PP and Hensley project 52" forward of the ball, so it really doesn't emulate a 5th wheel, depending on how much rear overhang the TV has.

But, I'm confused as to what that has to do with your original point and my response.

[Spaggs]

Just talked to Brent at ProPride. I don’t know if the call was productive or not. I asked if I could return my 1400s for the 1000s. I cited the info provided by you guys, who are much smarter than I am, some of whom are Engineers, pertaining to the 1400s being too stiff which may result in some popped rivets. He asked me for the link to this thread and said he was going to settle this ambiguity once and for all (paraphrased). He said that in no way are the 1400s too stiff and I don’t have to worry about popped rivets.
Thought I’d give you guys a heads-up for trial prep.

[dznf0g]

Originally Posted by Spaggs

Just talked to Brent at ProPride. I don’t know if the call was productive or not. I asked if I could return my 1400s for the 1000s. I cited the info provided by you guys, who are much smarter than I am, some of whom are Engineers, pertaining to the 1400s being too stiff which may result in some popped rivets. He asked me for the link to this thread and said he was going to settle this ambiguity once and for all (paraphrased). He said that in no way are the 1400s too stiff and I don’t have to worry about popped rivets.

Thought I’d give you guys a heads-up for trial prep.

That's good. Is he familiar with the AS front end issues? 1400s definitely are not as flexible as 1000s.

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[dznf0g]

Originally Posted by dznf0g

That's good. Is he familiar with the AS front end issues? 1400s definitely are not as flexible as 1000s.

Sent from my SM-G950U using Airstream Forums mobile app

Sean used to participate frequently here on the forum. He is an engineer. I am sure he is much busier than he was in those days, but it would be really nice if he would chime in. Do we know if Brent is an engineer?
I have burning and pointed questions, for which I can find no answers on the net.

[Spaggs]

Brent is not an engineer. He said so himself. I’ll call him tomorrow and ask if he can get Sean to participate in this discussion and leave knuckle draggers, like myself, to watch.

[uncle_bob]

Originally Posted by dznf0g

5th wheel pin location is at, or slightly ahead of the rear axle centerline. PP and Hensley project 52" forward of the ball, so it really doesn't emulate a 5th wheel, depending on how much rear overhang the TV has.

But, I'm confused as to what that has to do with your original point and my response.

Hi

You stated:

"If one has downward head tilt, then there is definitely an interaction between WD and sway control. No head tilt, no interaction....or maybe influence is a better word"

That is not correct.

The Hensley and Propride folks both calm to be "emulating" a 5th wheel via their mechanical magic. The 5th wheel is said to have total immunity to sway. It's all geometry in the horizontal plane. Vertical plane does not get into it.

This is talking about sway ( oscillation that puts you in the ditch) and not about porpoising (which is a completely different thing).

Bob